1. Field of the Inventive Concept
The present inventive concept relates to lithography. More particularly, the inventive concept relates to optical proximity correction (OPC) of masks used in photolithographic processes.
2. Description of the Related Art
Photolithography is a process by which patterns, e.g., circuit patterns, are transcribed onto a substrate such as a semiconductor wafer. In general, in photolithography, a photosensitive film (photoresist) is formed on the wafer, the photoresist is exposed to an image of patterns of a mask (e.g., a photomask), and the photoresist is developed to remove the exposed or unexposed portions thereof. Then, the resulting photoresist pattern is used as a mask to etch a target layer under the photoresist pattern and thereby form the circuit patterns.
The mask pattern and exposure conditions of the photolithography process must be designed such that the circuit patterns formed on the wafer bear a precise resemblance to the designed layout of the circuit patterns. However, the circuit patterns formed on the wafer may differ from their designed layout due to diffraction of the exposure light transmitted from certain regions of the mask where the mask patterns are complex or from regions of the mask where the size and line width, for example, of adjacent mask patterns have large differences. One technique used to obviate this problem is optical proximity correction (OPC). OPC is a predictive modeling technique in which a region of a mask having patterns whose image will not be transferred to the wafer precisely as desired will be predicted after designing the mask, and the shape of those mask patterns is altered, in their final design, based on the OPC model to compensate for differences between the design layout of the circuit patterns and the circuit patterns otherwise produced using the unaltered mask patterns.